Three-dimensional NAND flash memory devices can be used in imaging products, removable storage products, enterprise and client solid state devices, and embedded memory devices. In order to achieve high density at a lower cost, the pitch of memory openings should be reduced, and the number of word lines in an alternating stack of insulating layers and word lines should be increased. This increases the complexity of the etch process for forming memory openings and the metal replacement process employed to form the word lines. Use of multi-tier structures for the three-dimensional NAND memory devices further increases complexity in the manufacturing process.